1. Field of the Invention
The present invention relates to a highly efficient hybrid Hepatocyte Growth Factor (HGF) gene which simultaneously expresses two heterotypes of HGF.
2. Related Art
The present invention relates to a hybrid HGF gene prepared by inserting an inherent or foreign intron between exons 4 and 5 in HGF cDNA, which has higher expression efficiency than HGF cDNA and simultaneously expresses two heterotypes of HGF and dHGF (deleted variant HGF).
HGF is a heparin binding glycoprotein called a scatter factor. A gene encoding HGF is located at chromosome 7q21.1 and comprises 18 exons and 17 introns, having the nucleotide sequence of SEQ ID NO: 1 (Seki T., et al., Gene 102:213-219 (1991)). A transcript of about 6 kb is transcribed from the HGF gene, and then, a polypeptide HGF precursor consisting of 728 amino acids is synthesized therefrom. Simultaneously, a polypeptide of dHGF precursor consisting of 723 amino acids is also synthesized by an alternative splicing of the HGF gene. The biologically inactive precursors may be converted into active forms of disulfide-linked heterodimer by protease in serum. In the heterodimers, the alpha chain having a high molecular weight forms four kringle domains and an N-terminal hairpin loop like a preactivated peptide region of plasminogen. The kringle domains of a triple disulfide-bonded loop structure consisting of about 80 amino acids may play an important role in protein-protein interaction. The low molecular weight beta chain forms an inactive serine protease-like domain. dHGF consisting 723 amino acids is a polypeptide with deletion of five amino acids in the 1st kringle domain of the alpha chain, i.e., F, L, P, S and S.
It has been recently reported that both of HGF and dHGF have several biological functions, e.g., promoting the growth and morphogenesis of epithelial cell, melanocyte and endothelial cell. However, they are different in terms of immunological or biological properties.
For example, HGF shows about 20-fold, 10-fold and 2-fold higher activities than dHGF in promoting DNA synthesis in human umbilical cord venous endothelial cell, arterial smooth muscle cell and NSF-60 (murine myeloblast cell), respectively. dHGF shows about 3-fold and 2-fold higher activities than HGF in promoting DNA synthesis of LLC-PK1 (pig kidney epithelial cell), and OK (American opossum kidney epithelial cell) and mouse interstitial cell, respectively. HGF has a 70-fold higher solubility in PBS than dHGF. Several anti-dHGF monoclonal antibodies recognize only dHGF, but not HGF or a reduced form of dHGF, which implies structures of HGF and dHGF are different. Accordingly, the simultaneous synthesis of HGF and dHGF in vivo suggests that they biologically interact with each other (Shima, N. et al., Biochemical and Biophysical Research Communications 200:808-815 (1994)).
HGF secreted from mesoderm-derived cells has various biological functions, e.g., 1) inducing epithelial cells into a tubular structure; 2) stimulating vascularization from endothelial cells in vitro and in vivo; 3) regeneration of liver and kidney, owing to its anti-apoptosis activity; 4) organogenesis of kidney, ovary and testis; 5) controlling osteogenesis; 6) stimulating the growth and differentiation of erythroid hematopoietic precursor cells; and 7) axon sprouting of neurons (Stella, M. C. and Comoglio, P. M., The International Journal of Biochemistry & Cell Biology 31:1357-1362 (1999)). Based on these various functions, HGF or a gene encoding HGF may be developed as a therapeutic agent for treating ischemic or liver diseases. Actually, in vivo, the HGF may exist as either HGF or dHGF, and therefore, the coexpression of HGF and dHGF is important for maximizing the therapeutic effect. Accordingly, the present inventors have endeavored to develop a hybrid HGF gene which can simultaneously express HGF and dHGF with a high efficiency for gene therapy.